Genetic risk evaluation for chronic diseases such as Huntington's Disease or cancer includes searching for specific genes or mutations that cause disease or allow it to develop. Under the right conditions, identification of this risk can be useful in reducing uncertainty and in the case of negative, risk lowering results, can alleviate anxiety and unnecessary worry and preparation. In the case of risk-enhancing positive results, the benefits of reduced uncertainty, the opportunity to prepare, cope, and or prevent or detect disease early should reduce distress, but increased threat associated with the increased likelihood of serious or fatal illness may outweigh and overwhelm these benefits. The proposed research will evaluate the extent to which genetic risk testing enhances or attenuates chronic stress, how it affects mental health and quality of life and the conditions under which reduced uncertainty and the availability of coping options predict the impact of risk evaluations. The proposed research will measure stress, quality of life, mental health,and health behaviors as a function of high risk status and genetic risk evaluation for Huntington's Disease, Breast Cancer, and Multiple Endocrine Neoplasias. Short and long term responses to testing will be compared across disease characteristics, coping, social or personal resources, and frequency of intrusive thoughts. Consistent with a model in which benefits of reducing uncertainty are weighed against the threats associated with knowing one is at high risk for serious illness, it is expected that positive (higher risk) results will have greatest negative impact among those at risk for Huntington's Disease, because no options exit for prevention or surveillance. For breast cancer, positive results should not reduce distress but may not increase it appreciably, as relatively little uncertainty is reduced and several prevention/surveillance options exist. Distress may not decrease appreciably with negative results as the relieving news cannot rule out one's chances of developing breast cancer. For endocrine cancer, where both uncertainty reduction and surveillance options are maximized, positive results should be associated with stress reduction.